The disclosure of Japanese Patent Application No. HEI 11-222815 filed on Aug. 5, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to direct-fuel-injection-type spark-ignition internal combustion engines and to methods of controlling the internal combustion engine. More particularly, the invention relates to direct-fuel-injection-type spark-ignition internal combustion engines which effectively gasify fuel that has adhered to a cylinder bore and to methods of controlling the internal combustion engine.
2. Description of Related Art
A direct-fuel-injection-type spark-ignition internal combustion engine has a fuel injection valve which directly injects fuel into a cylinder. In this engine, fuel injected into a cylinder in the latter half of a compression stroke is gasified, and a combustible mixture with good ignitability is formed only in the neighborhood of an ignition plug at the time of ignition. Thereby stratified charge combustion wherein a lean mixture can burn is realized in the cylinder as a whole.
In stratified charge combustion, fuel injected into the cylinder in the latter half of a compression stroke has to be gasified at the time of ignition. For this purpose, a certain period needs to be ensured from the end of fuel injection to ignition. Thus, it is impossible to inject a large amount of fuel in the latter half of a compression stroke. At the time of high rotational speed and high load when at least a large amount of fuel is required, stratified charge combustion is prohibited, and a large amount of fuel is injected in an intake stroke to realize homogeneous combustion wherein a homogeneous mixture is formed in the cylinder at the time of ignition (see Japanese Patent Application Laid-Open No. HEI 10-299539).
In such a direct-fuel-injection-type spark-ignition internal combustion engine, the fuel injection valve is disposed at a periphery of an upper section of a cylinder so as not to interfere with intake and exhaust ports or an ignition plug located in the upper section of the cylinder. In general, for the purpose of forming a combustible mixture in the neighborhood of the ignition plug during stratified charge combustion, fuel injected from the fuel injection valve is deflected towards an area in the neighborhood of the ignition plug by means of a cavity formed in a top face of a piston. Thus, fuel is injected diagonally downward from the fuel injection valve so that fuel injected in the latter half of a compression stroke travels into the cavity at a piston position at the time of the injection.
If a relatively large amount of fuel is injected from such a fuel injection valve in an intake stroke during homogeneous combustion, fuel injection is inevitably carried out also in the latter half of the intake stroke. The fuel injected at this moment collides with the cylinder bore instead of the top face of the piston. Part of the fuel that has collided with the cylinder bore adheres to the cylinder bore. Because the entire cylinder bore has been cooled by coolant, this adherent fuel remains where it is without being sufficiently gasified, and thus does not contribute to combustion.
Thus, during homogeneous combustion, a more than necessary amount of fuel needs to be injected to compensate for the fuel that is not gasified. For this reason, there is caused a problem of deterioration of fuel consumption rate or a problem of dilution of engine oil by the adherent fuel.
Thus, in a direct-fuel-injection-type spark-ignition internal combustion engine which has a fuel injection valve directly injecting fuel into a cylinder and which switches its combustion mode in accordance with an operating state of the engine between stratified charge combustion caused by fuel injection in the latter half of a compression stroke and homogeneous combustion caused by fuel injection in an intake stroke, even if fuel injected in the latter half of an intake stroke collides with a cylinder bore and is adhered thereto, the invention aims to effectively gasify this adherent fuel.
In order to address the aforementioned problems, a first aspect of the invention provides a direct-fuel-injection-type spark-ignition internal combustion engine comprising a fuel injection valve which has a nozzle hole directed towards a portion opposed to the nozzle hole in a lower section of the cylinder bore so that fuel can be injected from an upper section of the cylinder into a cavity formed in a top face of a piston, and a cooler which cools the cylinder bore. The cooler cools the cylinder bore so as to suppress a fall in temperature of at least one area of the cylinder bore adjacent to the impingement portion in comparison with a fall in temperature of the other area of the cylinder bore than at least one area adjacent to the impingement portion.
The cooler may have a first cooling portion and a second cooling portion. The first cooling portion cools an area close to the upper section of the cylinder bore. The second cooling portion cools at least an area close to the portion opposed to the nozzle hole in the lower section of the cylinder bore. The second cooling portion has a lower cooling capacity than the first cooling portion.
The cooler includes a coolant passage, and the coolant passage in an area close to the portion opposed to the nozzle hole is smaller in cross-section than the coolant passage in an area close to the upper section of the cylinder bore. Because of this construction, the cooler located at least in the area close to the portion opposed to the nozzle hole in the lower section of the cylinder bore has a lower cooling capacity than the cooler located in the area close to the upper section of the cylinder bore. Therefore, the occurrence of overheating is prevented by sufficiently cooling the upper section of the cylinder bore. Even if fuel injected in the latter half of an intake stroke during homogeneous combustion collides with the portion opposed to the nozzle hole in the cylinder bore and adheres thereto, the adherent fuel can be effectively gasified.
While the cooler is provided in an area close to the upper section of the cylinder bore, there may be no such cooler provided at least in an area close to the portion opposed to the nozzle hole in the lower section of the cylinder bore. Therefore, the occurrence of overheating is prevented by sufficiently cooling the upper section of the cylinder bore. Even if fuel injected in the latter half of an intake stroke during homogeneous combustion collides with the portion opposed to the nozzle hole in the cylinder bore and adheres thereto, this adherent fuel can be effectively gasified.
The cooler may include the coolant passage having a first passage extending at least in an area close to the portion opposed to the nozzle hole in the lower section of the cylinder bore and a second passage extending at least in an area close to the upper section of the cylinder bore. A control valve is disposed in the first passage. The first passage is independent of the second passage. During the homogeneous combustion, an opening degree of the control valve is reduced in comparison with an opening degree of the control valve during the stratified charge combustion, whereby an amount of coolant flowing through the first passage is reduced. Therefore, the occurrence of overheating is prevented by sufficiently cooling the upper section of the cylinder bore. Even if fuel injected in the latter half of an intake stroke during homogeneous combustion collides with the portion opposed to the nozzle hole in the cylinder bore and adheres thereto, this adherent fuel can be effectively gasified.
The cooler includes a coolant flow passage having a first passage extending in an area close to a side opposed to a nozzle hole of the fuel injection valve in the cylinder bore and a second passage extending in an area close to a side opposite the side opposed to the fuel injection valve in the cylinder bore. A control valve is disposed in the first passage. The first passage is independent of the second passage. During the homogeneous combustion, an opening degree of the control valve is reduced in comparison with an opening degree of the control valve during the stratified charge combustion, whereby an amount of coolant flowing through the first passage is reduced. Thus, the upper section of the cylinder bore on the side opposed to the nozzle hole of the fuel injection valve is not sufficiently cooled. However, this does not mean that the upper section of the cylinder bore is always insufficiently cooled. That is, the upper section of the cylinder bore is sufficiently cooled during stratified charge combustion. Therefore, the occurrence of overheating is prevented. Even if fuel injected in the latter half of an intake stroke collides with the portion opposed to the nozzle hole in the cylinder bore and adheres thereto, this adherent fuel can be effectively gasified.
The cooler may include a coolant passage having a first passage extending in an area close to a side opposed to a nozzle hole of the fuel injection valve in at least two of the cylinder bores and a second passage extending in an area close to a side opposite the side opposed to the nozzle hole of the fuel injection valve in the at least two cylinder bores. A coolant inlet portion is provided at one end of the second passage. A coolant outlet portion is provided at one end of the first passage. The other end of the first passage communicates with the other end of the second passage. There is provided a communication passage which extends between the two cylinder bores and through which the first passage communicates with the second passage. A control valve is provided in the communication passage. During the homogeneous combustion, an opening degree of the control valve is reduced in comparison with an opening degree of the control valve during the stratified charge combustion, whereby an amount of coolant flowing through the communication passage is reduced. Thus, high-temperature coolant, which has flowed through the second passage during homogeneous combustion and cooled the cylinder bores on a side opposite the side opposed to the nozzle hole of the fuel injection valve, flows through the first passage. Hence, the cylinder bores on the side opposed to the fuel injection valve are not sufficiently cooled. Even if fuel injected in the latter half of an intake stroke collides with the cylinder bores on the side opposed to the nozzle hole of the fuel injection valve and adheres thereto, this adherent fuel can be effectively gasified. During stratified charge combustion, coolant flows through the communication passages, whereby low-temperature coolant is supplied to the first passage. As a result, the cylinder bores on the side opposed to the fuel injection valve are sufficiently cooled. This means that the cylinder bores on this side are not always insufficiently cooled. Thus, the occurrence of overheating is prevented.
Furthermore, according to a method of controlling a direct-fuel-injection-type spark-ignition internal combustion engine of another aspect of the invention, a cylinder bore is cooled, and a fall in temperature at least in an area close to the portion opposed to the nozzle hole in the lower section of the cylinder bore is suppressed in comparison with a fall in temperature in an area close to the upper section of the cylinder bore.
Also, according to a method of controlling a direct-fuel-injection-type spark-ignition internal combustion engine of another aspect of the invention, a cylinder bore is cooled, and a fall in temperature in an area close to a side opposite a side opposed to the nozzle hole of the fuel injection valve in the cylinder bore is suppressed in comparison with a fall in temperature in an area close to the side opposed to the nozzle hole of the fuel injection valve in the cylinder bore.
According to the aforementioned control methods, the occurrence of overheating is prevented by sufficiently cooling the upper section of the cylinder bore. Even if fuel injected in the latter half of an intake stroke during homogeneous combustion collides with the portion opposed to the nozzle hole in the cylinder bore and adheres thereto, the adherent fuel can be effectively gasified.